The demand for higher performance, amplifier, reference and sensor devices for use in communication, instrumentation and processing applications continues to increase. For example, designers and manufactures of such applications are requiring for the accuracy of the components and devices, such as operational amplifiers (“op amps”), current and voltage references, and temperature sensors and the like, to be continually improved to meet the higher performance requirements of a myriad of emerging audio, video, imaging and wireless applications.
Op amps, references, sensors and other similar types of devices typically are varied and adjusted through trimming techniques to improve the precision and accuracy of the devices. In many instances, a current source within such devices is trimmed at the wafer level before packaging in which extra pads are utilized. After packaging trimming requires a different technique. For example, with reference to an electronic package 100 illustrated in FIG. 1, a current source 102 needs to be trimmed after being packaged with a device, such as an op amp 104. Monitoring the progress of the trimming process requires sensing a change in the magnitude of the trimmed current source 102.
One method for sensing a change in the magnitude of the trimmed current source is to steer a replica of the trimmed current to an additional package pin, i.e., in addition to the ground GND, power PWR, and input/output pins, and then externally monitor the current. Requiring an additional pin is less desirable in modern micro-sized packaged devices.
Another method for monitoring the progress of the trimming process, implemented without the need for an extra package pin, includes the creation of a dual function on an existing package pin. For example, with reference to an electronic package 200 illustrated in FIG. 2, a dual function pin DUAL is configured for providing a positive terminal to an op amp 204 as well as for delivering a replica of current from a current source 202 to an external measurement system. While such a technique is conducted without the need for an extra package pin, the technique is susceptible to measurement errors. For example, if the target value of the adjusted current source is sufficiently small, any leakage current, such as from a switch circuit 206 or from an electro-static discharge (ESD) protection circuit, can alter the value of the replica current delivered to dual function pin DUAL. As a result, an error is added to the measurements resulting in a reduced accuracy in the trimming technique.